Hyperthyroidism in cats

Hyperthyroidism is excess production of thyroid hormones, which increases the body’s metabolism.

Most hyperthyroid cases are due to a benign tumour on the thyroid gland. If left untreated, they can negatively impact a cat's weight, blood pressure, heart, vision, liver and kidneys.

What are common hyperthyroidism signs in cats?

Early signs include:

  • Unkempt appearance
  • Increased appetite
  • Restlessness or vocalisation
  • Lethargy, and rarely, poor appetite

Intermediate or advanced signs include:

  • Weight loss 
  • Increased thirst and urination
  • Vomiting 
  • Diarrhoea
  • Blindness
  • Sudden death


How is hyperthyroidism managed in cats? 

Hyperthyroidism management can involve various approaches. Radioactive iodine therapy can destroy the tumour and is often curative. Surgery to remove the tumour is no longer routinely performed. 

Daily medication to inhibit thyroid production can be effective, but is lifelong, requires diligence, and regular diagnostic monitoring. A strict low-iodine prescription diet can also inhibit thyroid production, with varying results. 

Discussing a personalised management plan with your veterinarian is important for the best outcome for your cat. Regardless of the treatment plan chosen, regular vet visits and diagnostic testing are required to monitor treatment response. 

Weight loss could be a sign of hyperthyroidism in cats.


What is the prognosis for cats?

The prognosis depends on your cat’s response to the chosen management plan. Overall, well-controlled hyperthyroid cats can have a good quality of life, and a normal lifespan, but some may eventually develop chronic kidney disease.  

Management tips for a cat with hyperthyroidism

At-home needs include:

  • Easy access to food, water and a clean litter box
  • Consistency with any prescribed medications, which can be compounded for easier administration
  • Strict adherence to a low-iodine prescription diet, if recommended by your vet
  • Monitoring appetite, drinking, urination, defecation, weight and energy levels

For end-of-life care:

In a crisis:

Immediately contact your vet if your cat has uncontrollable vomiting or diarrhoea, difficulty breathing or walking, is vocalising in pain, or collapses.

It is vital to begin end-of-life care discussions before your cat’s condition becomes unmanageable, or they begin losing their quality of life. 

The team at Goodbye Good Boy offers individualised support to help you and your family navigate this difficult time by providing quality-of-life checks, in-home euthanasia, cremation and aftercare services, and personalised memorialisation options. Our services can even be pre-paid to help ease the financial burden at the time of your pet’s passing. 


To learn more about our pet end-of-life services, give us a call on 1800 953 619 or visit our website goodbyegoodboy.com.au.



This article was reproduced with permission from Goodbye Good Boy advisor Dr Dani McVety, of Lap Of Love.